Treat Goldfish Mouth Rot

There should be little confusion about what mouth rot is; the name pretty much sums up what the goldfish disease will look like. In order to treat this through, it requires knowing what causes the mouth of a sick goldfish to rot.

Goldfish Mouth Rot Symptoms

  • Goldfish will rub their mouths and noses against objects
  • The mouth of the sick goldfish becomes red
  • The lips then begin to separate from the mouth, pulling tissue apart.
  • The mouth might collapse in on itself leaving a gaping hole.

Mouth Rot Caused by Columnaris (Cottonmouth)

  • White spots appear on the mouth of the goldfish
  • Cotton-like growth will begin to grow.
  • The mouth will rot away.

Effective Treatment

You can treat with API PIMAFIX and Aquarium Salt.

Professional Treatment Option

  • When goldfish mouth rot begins to show, use a cotton ball to swab the infected area with hydrogen peroxide.
  • Then an injection of Baytril is recommended.
    • If an injection is beyond your expertise (hint: it probably is), treat mouth rot with antimicrobial medication. Potassium Permanganate, Fish Mox (Amoxicillin) is an effective option.
  • You can also add some Aquarium Salt.
  • Remove the sick goldfish and quarantine it so it can heal without being picked on by other fish.
  • Finally, add a slime coat protector


Goldfish mouth rot is the result of bacterial infection but it typically starts due to the presence of a parasite. It’s best to check for parasites first and treat them accordingly.


You can help prevent mouth rot by keeping stock numbers lower. This will lessen the likelihood of scraping their mouths on objects. It’s also important to keep the water clean and regularly test the water quality.

Reviewed By: Tim Winter

Tim Winter has a strong affection for pets and wildlife. His years of experience caring for various types of pets has led him to share his knowledge with others on the best practices in pet care. Tim holds a Bachelor of Science from the University of Oregon School of Journalism and Communications.

10 thoughts on “Treat Goldfish Mouth Rot”

  1. its my first time getting a goldfish, and i think he has red mouth disease he isnt eating properly and his lips have fallen, i dont know if im too late but what am i supposed to do? im freaking out

  2. I was curious, I’ve been treating my goldfish for 4 days now and the infection stopped, but does the mouth begin to heal back or is he going to be missing half his mouth. I’ve had him almost 3 years and he’s such a lively little guy. I usually keep him in a 60 gallon community tank, but right now he’s in my medical tank.

  3. My Goldfish’s mouth had turned red and white with swelling .Help me !!!! I am very scared.i had already lose one gold fish because of thIs .help me. I love my goldfish

  4. My slim fish has mouth rot. I used hydrogen peroxide on his mouth to try to prevent it gwtting worse. I just need to know how often i should be doing it because i dont want to hurt him i want to help him. Your opinion would be greatly appreciated! Thank you

    • you can buy a broad spectrum medication from any local pet or fish store. Ask the fish expert for a mouth rot treatment. Aquarium salt might also help with the healing.


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